2 Pallas (pal'-us, Greek Παλλάς) was the first asteroid discovered after 1 Ceres. It was found and named by H. Wilhelm Olbers on March 28, 1802.

Name

The asteroid is named after Pallas, the daughter of Triton and friend of Athena in Greek mythology. (There are several male characters of the same name in Greek mythology, but the first asteroids were invariably given female names.)

Pallas is the third largest main belt asteroid, similar to 4 Vesta in volume (to within uncertainty), but significantly less massive.

Pallas is currently the largest Solar System body (barring trans-Neptunian objects) whose surface has not been directly imaged by spacecraft or telescopes. It may also be the largest irregularly-shaped body, meaning that it has not been compressed by gravity into a spheroid shape (other candidates may be trans-Neptunian objects such as 2003 EL61).

Pallas also has unusual dynamical parameters for such a large body. Its orbit is highly inclined and somewhat eccentric despite being located in the central part of the Main belt.

Furthermore, its axial tilt is very high, being around 70° (in fact estimates vary from 56° to 81°) [4][7]. This means that, every palladian summer and winter, large parts of the surface are in constant sunlight or constant darkness for a time of the order of an Earth year. Consensus has not been reached as to whether Pallas' rotation is prograde or retrograde, but one of the poles points in a direction around right ascension 5 h, declination +6°, with a 25° uncertainty [4].

There are indications that the surface composition of Pallas is very similar to the Renazzo carbonaceous chondrite meteorite [8].

Observations

Some notable observation milestones for Pallas include:

Pallas has been observed occulting a star several times, including the best observed of all asteroid occultation events on May 29, 1983, when careful occultation timing measurements were taken by 140 observers. These have helped determine an accurate diameter [5]. During the occultation of May 29, 1979 the discovery of a possible tiny satellite with a diameter of ~1 km was reported. However, it has not been confirmed. In 1980, speckle interferometry was reported as indicating a much larger satellite with a diameter of 175 km, but the existence of the satellite was later refuted. [3]

Radar signals from spacecraft in orbit around Mars and/or on its surface have been used to estimate the mass of Pallas from the tiny perturbations induced by it onto the motion of Mars [1].

There have not been any telescopic observations of Pallas that have resolved any features on its disk. Pallas has not yet been visited by a spacecraft, but if the Dawn probe is successful in studying 1 Ceres and 4 Vesta, its mission may be extended to Pallas.

Trivia

The chemical element palladium (atomic number 46) was named after Pallas.